High-frequency spot heater



May 9, 1950 P. D. zoT'Tu HIGH-FREQUENCY SPOT HEATER 5 Sheets-Sheet l Filed May 20, 1944 mr y V0 n mZ W a w# u n w p .W7 Y1U B wm.

n ww. wm Q May 9,195@ RDZQTTU Y 2,506,626

HIGH-FREQUENCY SPOT HEATER Filed May 20, 1944 5 Sheets-Sheet 2 n JNM /lo I m /5 fm i A/z /x (55 `f55a K fi v22 /7 w f R f (55a (56 L25 l A l 6% La 7 d" C INVENTOR.

May 9, 195o l P. D. 'zo-m1 2,5%,626

HIGH-FREQUENCY SPOT HEATER Filed May 20, 1944 5 Sheets-Sheet 5 IN1/EN TOR. P60/ Z@ Ww.

filo/UEM Patented May 9, 1950 UNITED STATES TENT OFFICE HIGH-FREQUENCY SPOT HEATER Paul D. Zottu, indian Hills, Ky., assignor to The Grdler Corporation, Louisville, Ky., a corporation of Deiaware Application May 20, 1944, Serial No. 536,629

Claims. i

This invention relates to high-frequency systems of the type adapted for the production of heat within dielectric materials and has for an object the provision of a relatively simple, eidcient, method and means ior producing a substantial amount of heat within a relatively small area.

Though the invention has many applications, it has been found particularly useful in connection with gluing operations of various kinds. Where -plywood or other flexible but resilient material is to be adhesvely secured to an irregular or curved surface, it has been found advantageous to spot glue the plywood at various `points to hold it in shape. Thereafter the glue line as a whole may be dried or hardened.

In carrying out the invention in one form thereof, a high-frequency spot heater comprising a concentric or coaxial circuit is utilized. One end oi` the coaxial circuit may be conductively connected together while the inner and outery conductors are spaced one from the other at the opposite end to form electrodes. A high-voltage high-frequency electric eld is lproduced between between the exciting coil and the coaxial circuit.

Further in accordance with the invention, the coaxial circuit is embodied in a shape which conveniently serves as a hand tool. It may be provided with a .pistol grip which extends from the outer conductor, and through which handle or grip both the high-frequency supply line and circuit-controlling conductors may extend.

For a more detailed explanation of the invention, and for furtherA objects and advantages thereof, reference is to be had to the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a sectional elevation of a spot heater;

Fig. 2 is a sectional view taken on the line 2 2 of Fig. 1;

Fig. 3 is a fractional side elevation o a modirled form of the invention as applied to a gun of 'the same type as shown in Fig. 1;

surface of the outer conductor lil.

tal

Fig. 4 is a fractional side elevation of a modied head comprising the active electrodes;

Fig. 5 is a sectional view taken on the line 5-5 of Fig. 4;

Fig. 6 is a sectional view of a further modification of the head, showing a different form of electrodes;

Fig. 7 is an end view of Fig. 6 taken in the direction of the arrows 'l-'l of Fig. 6;

Fig. 8 is a sectional View taken on the line 88 of Fig. 6; and

Fig. 9 diagrammatically illustrates a wiring diagram of a typical system embodying the invention.

Referring to the drawings, the spot heater or spotter gun of Fig. 1 comprises a concentric or coaxial circuit having an outer conductor iii and an inner conductor II. The inner conductor is supported coaxially of the outer conductor by means of a closure i2 for one end of the outer conductor Hi and a disc I3 of insulating material, such as mica, which at its center supports a bearing member I4. The outer portions of the disc i3 are fastened by screws Illa to lugs E5@ of an adapter I5, only two of which lugs are shown in Fig. 1. One end oi the inner conductor il extends outwardly through the closure l2 and has secured to it an operating knob I6. Supported on a threaded portion Ila of the inner conductor is a movable contact member Il', having a hub Ila which threadedly engages the threaded portion ila. The contact member il is provided with a lplurality of resilient :lingers or contact memlbers I3 which are resiliently biased against the inner It will be observed that the contact member il is provided with a slot through which extends a guiding member Z secured in place as by means of screws 2l. The guide member 2B lprevents rotation of the Contact member ll when the inner conductor l l is rotated by 4means of the knob i6. The hub Ilo. has extending from it a plurality of contact members or ngers 22 which engage the unthreaded portion lib of the inner conductor Il. It will thus be seen that the contact menrber l1, upon rotation of the knob i6 and the inner conductor il, is moved longitudinally of the coaxial line. Inasmuch as contact member l'l conductively interconnects the outer and inner conductors le and H, the effective length of the coaxial line is varied in accordance with the position of the contact member I1.

It is to be further observed the contact member i7 has the lower section cut away to make room for an exciting coil 23, shown in the form of a ing both'inductance y:and capacitana- Y fsemantiektuninaranee With-substantial Changes single loop, one end of which is plvotally mounted in a terminal post 2li, while the opposite end is carried by an adjusting rod 25 journalled in the closure I2. The end of theirocl 25 is provided with a slot 25 for cooperation with any suitable means, such as a screw driver. Also, by means of such a screw driver, a locking set screw 2 may be released and the rod-25 Lthen rotatedjtorotate the exciting coil 23 to diierent angular positions, such as shown by the broken lines in Fig. 2.

The forward end of the cylindrical conductor I is fastened by means of screws 3u tothe'adapter I5. The adapter I has a peripheral iiange lh which forms a stop or shoulder against which the end of the conductor :I0 A'may abut. The' adapter I5 is also provided with a flat plate-like extension 45o through an opening of nwhic-hthe inner conductor I I extends. The plate I5@ forms in combination with a second plate-like member 32 a capacitor. To vary the capacitance the spacing'may be varied.,- and the plate '3-2 may be. cupshaped, withv the cuter lip ori-ange-Bza. extending `parallel vto-but in-spaced'relation with theinner surface of the outer conductor ID. The adapter hI/has secured to ita-n operating head 33. `Preferably the head '33 is provided with-several, for example three, bayonet slots through one ofy which -fthereeXtendsrthe fastening screw 3. A pin=may extend through .the otherbayonet slots (neither of which .isshownL 'The'headt from the. coupling I5, is of conical shape, the sides approach- 'iingfeach other, orithe outer wallbeing of progressively decreasing diameter so as Yto lleave an annular space 35a between the head 33, which with radapter '15 forms an V extension of .theouter conductor 1li), and the vend 3 5 Vof fanfelectrode;

:iorrnso a cable 3.8,1is electrically.connectedtdthe y terminal post Y211, which is itself fmounted upon 1an :insulating Vmember' "62. 'The grounded metallic eshielcl :ofthe cable .or line -35 is connected Vby rfrneans cia strap and screw-iidiitothe outer conductor ii. .By .ineansof these connections, the Thigh-frequency energygfiows through a circuitin- 'cluding inner conductor #i I ,the loop V23, the ad- `justing rodgithe outer conductor .-I t, and to .the ,:sheath 43. IThe loop 23 serves inductively to :couple the ,high-frequency, energy 'to i Vthe coaxial gun-circuit.

The coaxiall gun-circuit or coaxial line Yitself is tunedto rescnanccby'suitahle adjustment .tunedztofrescnancaztifnrmsa tank nimm,

:in-the applied frequency4 thev plate 32, :after releasing thegset screws, f may be mOVEd 'OW'ed 01' taaway fromthecouplingplateA i tcsubstantially to :change-the capacitanceof the coaxialgun-circuit.

For smaller changes, axial movement of the ymem- :fberi'l'i has the effectorchanging theinductance .oil-the line. Assho.wn,the.coaxial orconcentric line provides a resonant `circuit orhgh eiciency, 1

zal quarter wavelengths- .itsleneth may be equal @any .ei/er1 number 0f electrical quarter wavelengths. Y,Such a constructionrnay be desirable where-the source of highfrequency energy is to be appliedsimultaneously 4 or of high Q; that is, the ratio of the capacitive reactance to the resistance is very high, of the order of several hundred.

During normal operation, there is produced within the coaxial line or tank circuit circulation of energy in substantial amounts. The result is the production in the annular Vspace 35a of a highvoltage high-frequency electric iield :which may be used for heating purposes. It is only necessary to take the spot heater by the handle t0 and apply vxthe active end 33-35 of the concentric line to `thefrnaterialto 'be heated. After a few seconds, the high-frequency high-voltage electric eld established through the material to be heated and between the Acoplanar outer ends of conductors 33 and`35 will greatly elevate the temperature of ,mostdielectric materials. For drying, activating, or polymerizing adhesives, the spot heater has been found particularly eective.

Further in accordance with the invention, a control circuit is introduced through the handle a@ and byV means of a normally open switch :5i the .applicationcf vthe high-frequencytenergy `maybe controlled. rlhe switch -5I1is operatively -connected'to a trigger or push-buttonf52. .Upon .the application of pressure itc .the triggerY or -button 52, the switch 5I is closed and as will-.be ydescribed hereinafter, .produces operation 10i the high-frequency generator to .supply the spot vheater with energy.

,As shown in Fig. Lthe-spotheater comprising `the coaxial gun-circuit is fpreferably made ja quarter of an electrical wavelengthlong. By reason of the added capacity-providedfbygthewall of .conductori and the plates Y45e-and 3.2,'the spot heater is physically shortergihanaqurter .wayie length. The requirementis thatthe-,coaxial -circuit be at or near resonancefat the operating frequency. VIt is tobeunderstoodfthefspot heater may be made VAa yhalf wave length long, `in ,which case, both ends may be.madeddenticalwiththe oneincluding A,the head 3;3 and both ends may then function in -identical ;manner. -Insuch a caseneither end would beconductively connected .and the .high-frequency source -Of :supply @Ould be conductively Yor .inductivelvfapplied at any1-,se-

; lested ncntalone the length'offthe coaxial line. It is 4nirther pointed out Ythat the ,spot heater .when conductvely termnatedatone end may .be `Qf .a .length equal to any cdd number vof electri- If y not kso terrnir i atm edy to ltwo or more locations a substantial distance fi-rom each other.

'In the modification of Fig. 3, azplate 55 (corresponding with the plate ,320i Fig-,1) is threadedly mounted on a threaded section E6 ofthe inner `conductor II of the concentric line. The .plate ,hasresilient negers ,55a which .extend to and @engage the Unthreaded refiler; 0f the 01.1- ductor'ii. rlllnis provision eliminates ,the high- I frequenti? resistance da? to the .1611.1readsY and prf vides netter electrical contact. ,than may be b 1tainfes bythe threaded @erlesenen YThe disc .55 provided with e mich :intowhieh extends an ,odes of the valves 8B and 8|.

described, to apply high-frequency energy to the coaxial gun-circuit. This arrangement provides somewhat greater flexibility in that the gun may be tuned to resonance over a greater range of operating frequencies and the required tuning may be readily effected. In this modication, the member Il' may be fastened directly to the closure i2 and to the outer conductor l.

It will be further observed the active electrode 35 is resiliently mounted in a housing 5e and is -urged outwardly by means of a compression spring 6l). This resilient mounting is advantageous in that it insures intimate contact of the electrodes to the material being heated and serves to apply pressure to dielectric members being treated.

In the sectional view of Fig. 5, the adapter I5 is shown in more detail. This coupling member makes possible the use of different heads, such for example, as the one shown in Fig. 4. In this instance, the central electrode 6l is of substantially larger diameter than the electrode of Fig. 3. The outer conductor 62 is provided with any desired opening so that the annular space 63 may be selected or adjusted to meet the needs of the desired heat pattern. In each case, the adapter I5 of Fig. 5 and the head 52 of Fig. 4, both of conducting material, provide a continuation of the outer conductor IU. f

Other forms of heads may be utilized, such for example, as the one shown in Fig. 6. In this instance, the outer conductor t2 is cylindrical and of the same diameter as the conductor lil. In Figs. 3, 4 and 6, the length of each head is approximately the same, that is, the length from the adapter l5 to the end of each head. The modification of Fig. 6 includes seven inner electrodes t3, each of which is located in spaced relation with openings 64 in an end plate 55, secured to the conductor 62 as by the screws 66. The respective inner electrodes 63 are mounted on an insulated disc 'it with electrical conductors 7! extending from each electrode 63 to the tubular conductor 'it which is fastened to the inner conductor Il, Figs. 6, '7 and 8.

Though any suitable oscillator may be utilized, the oscillator or high-frequency generator illustrated in Fig. 9 has been found to be satisfactory. Preferably it comprises a push-pull oscillator. As shown, two electric valves 80 and 8l may be mounted within the same envelope 82. This double valve arrangement may be a Number 829 tube, or one of like character. Obviously, each tube or valve may be contained within its own envelope or several valves may be connected in parallel in each side of the push-pull amplifier, these modifications being well understood by those skilled in the art.

It will be observed the respective anodes are connected to the opposite ends S3 and 8d of a loop or coil 85 which at its electrical midpoint is connected by the conductor 8E to the posi- 'tive source of anode potential as indicated at B+. In accordance with the invention, the positive source of supply is connected directly to` ground as indicated at G. This provision is desirable to minimize personnel hazards. A second coil 8l in the form of a single loop is mounted vwith the electrical midpoint of coil t? connected by conductor 89 through a resistor 9i) and a shunting condenser el to the indirectly heated cath- It will also be observed the negative side of the source of anode supply is also connected to the cathodes as indicated at B.

The loop or coil plus the tube capacities plus the distributed capacitance forms a tank circuit of relatively high eincency and high Q. High-frequency energy is derived therefrom through a conductive connection, including a conductor 93 which is the inner conductor of the coaxial cable 38 previously referred to and which leads to the gun or the spot heater.

This spot heater is diagrammatically shown in Fig. 9 with the trigger 53 arranged to close a circuit for a relay 95 connected in series with a source of supply St. When the trigger 53 closes this circuit, the relay 95 serves to close the primary circuit for the B supply indicated at 91. The B supply is derived from any available source such as the usual volt, 60 cycle A. C. supply. The supply terminals are indicated at 9S and 99 whereas the B supply or anode current indicated on the box 91 as B-land B- corresponds with the similar terminals designated in like manner on the left-hand side of the diagram. When- ,A ever the pressure is removed from the trigger 53 the source of anode supply is de-energized by the opening of the relay 95 and when pressure is applied thereto, the relay 95 closes to energize the oscillator.

In accordance with the invention, the oscillator may be designed to produce high-frequency energy of any desired frequency. Frequencies ranging from to 200 megacycles, with a radio frequency output of 75 watts have been found satisfactory for a wide variety of applications of the spot heater.

Common to the several embodiments of the invention is the provision of the concentric circuit which in itself provides a tank circuit of high eiiciency.

In a typical embodiment of the invention, with energy applied having a frequency of 150 to 200 megacycles, the outer conductor I0 had a length of Gfe and an overall length from the conductively closed end of the line to the end of the electrode 35 of approximately 9". In this embodiment `of the invention, the outer conductor lil had an outer diameter of 2.125" and an inner diameter of 1.959". The inner conductor H had a diameter of T36 along the unthreaded portion thereof. In Fig. l, the threaded portion ila had a diameter of 3/8. This larger diameter extended approximately half-way of the spot heater. In Fig. 3, the inner conductor had a diameter of Tae, through the unthreaded portion and only a slightly larger diameter for the threaded portion.

While preferred embodiments of the invention have been described, it will be understood that further modications may be made without departing from the spirit and Scope of the invention as set forth in the appended claims.

What is claimed is:

l. A high-frequency spotter gun comprising a barrel forming the outer conductor of a concentric line, a second conductor, means supporting said second conductor within said barrel and in spaced relation therewith to form the inner conductor of said line, one end of said inner conductor lying approximately in the same planeas the corresponding end of said outer conductor for application to the work to be heated, said concentric line forming a resonant circuit for a given operating frequency, an input coil within said outer conductor and inductively coupled to said line, means including a pivotal support for said anca-'ese said-coil deivaryingftheecoupling of said Iedil/ith respectto-'sai'cl line by pivotal Ymovement er1-said coil within said outer conductor `to change-its -angul'ar relation with lrespect to vsaid-inner conductor, and-means -fforcvarying the electrical length offsaid line to produce resonance at a Selected operatingr frequency, thereby-.to produce -'between and inv '-thev-icini-ty` or the -coplanar ends Aof vsaid line a concentrated radio frequency iield.

Av2.Me'an'sfor producing aconcentiatecl highfrequenc'y `'electric iield between yand in the vicinity of an active inner'lelectrode and a grounded fouter electrode, comprising conductors forming tt-concentric line, vv'Corresponding ends of which V'lforlrn said :electrodes adapted to `'be applied -to said outer `'conductor-ior Y varying the position and rcoupling of said loop `withrespect tosaid innerv conductor.

3. Aspoth'eater comprising means for produc- -1ing =a Yconcentrated `high-irequency electric eld between and in the vicinity of an A-active inner electrode and a grounded outer electrode formed by -fcorresponding 'coplan'ar ends of Vconductors 4forming a concentric line, 'corresponding ends of lwhich conductorsform said :electrodes which 'are i'adapted'to |`be applied to work to be heated, 1a vplate lcarried by one of said electrodes-and extending adjacent the other of said electrodes to Vfiorrn a` capacitor "within*said line, means operable upon relative rotation 'of the conductors of ysaid concentric fl-ine for varying the `'capacity of said capacitor thereby to tune said line to Aresofnance fer a Iselected operating -requency, yand lmeans for supplying said rvline with high-fre- J 'quer-icy energy.

Je. -A rnaterialiheater comprising means for producing ya concentrated high-frequency electric field between andfin the vicinity of an active inn'er electrode-and -a grounded outer electrode for heating-material in contact with said electrodes, conductors-forming aconcentric line, correspond- Ting lends of which form said electrodes for applil Vcation to the material to be heated, a pair off randially extending' plates forming a capacitor withfin 'said line and -spaced from said-lendsV of said electrodes, means operable upon relative rotation of the conductors of said concentric line for varying the capacity of said capacitor by changi'ng the axial spacing of said plates'thereby to itune said line to resonanceforfa selected operating frequency, means including a coupling coil within said oiite1conductorfor inductively lsupplying said :line with high-'frequency energy1and means for varying the coupling of -saidcoil with lrespe'otto'said line. Y

- -irequ'ency spotter gun comprising a Vng the outer conductor of a concen- Lline, asecond conductor, means supporting second conductor within said harrel'in spaced relationtherewith to form the inner vconductor l*of said line, saidconcentric' line forming afresoinant vcircuit fior a given operating frequency, an #operating head forniedof an electrically conductf'in'g material, means forf'conductively attaching l'said head to said barrel-and for supporting the same therefrom, conductive means YeXtendifr-ig 1f-rom -sa-id inner conductorand iorming-in'c'oop- Y outer conductor ci 4fer-ation'-fwith the-*free end of said head the fend l:ofA said line at which there `is concentrated fe'lectric. field-o .high frequency to beapplied'to material to be heated, coupling means l:located -lietween said conductors for tuning said'concentrcline, and-means eirectively connected to said line -providing-anexternal connection to a-source of high-frequencyelectrical energy.

S6. IA 'high-frequency spotter-:gun comprising a barrel forming the outer conductor `cfa-concentric iine, second conductor, means supporting said second conductorfwithin saidbarrel infspaced vvrelation therewith 'to form the inner conductor of said line, an operating heado electrically conductive material,- .cylindrical v`supporting means for said head carried by one end ci said barrel,

said-head being cylindricalatene end and having a frustro-conical shapeiroms'aid cylindrical portion to the. opposite end thereof, an electrically vconductive extension for said inner conductor rforming with thesopen end'ofsaid headan end of said concentric line at which there .is uproduced concentrated electric iield of Vhigh 'frecuencyzto be applied to 'work to heated, coupling means located between saidiouterconductor y*and said :second conductor fortuning said line,

andmeans effectively connemed to said line providingian externalconnection.toza source of highfrequency electrical energy.

7. A spotter gun employing high-frequency electrical energylfcomprisingga lbarrel. forming :the

a concentric line, Vase/cond conductor, supporting said second conductor within 'said barrel Vand in Vspaced .relation ltherewith. to vform the inner conductor Vof 'said line, said concentric line forming a resonantcircuit fora given operating frequency, `means ifor .applying energy to Vsaid line, an operating head 'of electrically conductive .materia-l,lsupportingmeans vforfsaid head carried byone end of said harrel, an electrically conductive'extension for saidinner lconductor oriningwith the open end Yof said head at lleast one `extension of saidconcentric line in which ,therelis produced a concentric electric ield of high 'frequency ada Jted to be applied to work to be heated, said head and said extension of said inner conductor being removable for the substitution of cther'extensions and heads of Athesame length but of differing spacing between each said Aothe` extension andthe open end. of each said other head.

8. VHeating Vapparatus :employing high frequency electrical energy including pair of con- 'centrically spaced electrodesadapted to be .applied to the werkte he heated, coupling means located between said electrodes for tuning said kpair .of electrodes, and means `eiiectively connected to said electrodes prot-f. ing an lexternal connection to aseurce of said energy.

9. Heating apparatus employing 'high frequency electrical energy including a pair of .concentrically spaced electrodes having terminal portions lying substantially in a plane, coupling means `located between said electrodes for'tuning .said pair'of` electrodes to resonance at the oper- "said inner lconductor through Dsaid annular cong ductor for engagement with the work, and plate structure within said line adjustably to tune it to produce an intense high-frequency eld in the gap between said electrodes as pressed against the work.

PAUL D. ZOTTU.

REFERENCES CITED The following references are of record in the le of this patent: 10

UNITED STATES PATENTS Number Name Date 1,555,258 Alleutt Sept. 29, 1925 1,972,050 Davis Aug. 28, 1934 Y) 2,097,519 Gabriel et ai Nov. 2,1937 2,103,515 Conklin et al. Dec. 28, 1937 Number Name Date 2,163,898 Van Der Lande June 27, 1939 2,177,272 Zottu Oct. 24, 1939 2,234,556 George Mar. 11, 1941 2,242,404 Schussler May 20, 1941 2,253,503 Bowen Aug. 26, 1941 2,280,771 Dufour et al Apr. 28, 1942 2,308,043 Bierwirth Jan. 12, 1943 2,342,254 Dallenbach Feb. 22, 1944 2,364,526 Hansell Dec. 5,1944 2,370,883 Smith Mar. 6, 1945 2,422,525 Brown et al June 17, 1947 OTHER REFERENCES Taylor: A radio-frequency gun for spot-gluing wood, Electronics, November 1943. Pages 106" 111 and 310. 

